Unique [shortcode] Protected content message

This may be more of a feature request than an actual issue.

You can set up multiple shortcodes which is great but some content we want to be able to protect but also have a teaser message
Example of one that we have today

[shortcode]
Link to some custom content/ file etc
[/shortcode]

Maybe something like

[shortcode teaser="If you would like to learn more about the content please register" ]
Link to some custom content/ file etc
[/shortcode]

We basically have pdf files that are associated with various topics so our content authors want to be able to provide their own leadin/ teaser to entice anonymous users to register for free/extended content.

I was thinking about just writing an addon to support this. But didn't know if there was potentially something undocumented.